A solar cell or photovoltaic cell is a semiconductor device consisting of a large-area p-n junction diode, which in the presence of sunlight is capable of generating useable electrical energy. This conversion is called the photovoltaic effect.
Over 95% of all the solar cells produced worldwide are composed of the semiconductor material Silicon (Si). As the second most abundant element in earth's crust, silicon has the advantage, of being available in sufficient quantities, and additionally processing the material does not burden the environment. To produce a solar cell, the semiconductor is contaminated or doped. Doping is the intentional introduction of chemical elements, with which one can obtain a surplus of either positive charge carriers (p-conducting semiconductor layer) or negative charge carriers (n-conducting semiconductor layer) from the semiconductor material. If two differently contaminated semiconductor layers are combined, then a so-called p-n-junction results on the boundary of the layers.
At this junction, an interior electric field is built up which leads to the separation of the charge carriers that are released by light. Through metal contacts, an electric charge can be tapped. If the outer circuit is closed, meaning a consumer is connected, then direct current flows. Silicon cells are approximately 10 cm by 10 cm large (recently also 15 cm by 15 cm). A transparent anti-reflection film protects the cell and decreases reflective loss on the cell surface.
Solar cells have many applications. They are particularly well suited to, and historically used in, situations where electrical power from the grid is unavailable, such as in remote area power systems, handheld calculators, remote radiotelephones and water pumping applications. Solar cells (in the form of modules or solar panels) on building roofs can be connected through an inverter to the electricity grid in a net metering arrangement.
Monocrystalline Si is the base material to achieve the highest efficiency of Si based solar cells. However, monocrystalline Si in the form of wafers, i.e., circular discs in different diameters, typically 150, 200 or 300 mm, is expensive and its availability can be constrained due to high demand from the semiconductor industry.
Monocrystalline silicon, however, is also a limiting factor for the production of high efficient photovoltaic (PV) solar cells. The actual silicon layer thicknesses for PV applications are in the range of 200-330 μm. Efforts to reduce the thickness of the Si layers are typically limited by the ability to handle free standing layers of Si below the thickness range mentioned above.
A major disadvantage of the present PV cells is front side shadowing which has been identified as a main cause for reducing energy yield of grid-connected photovoltaic systems.